Chelsea are confident of signing John Stones from Everton amid interest from Manchester United.(Getty)

Chelsea are reportedly confident of signing Everton defender John Stones during the ongoing transfer window, according to ESPN.

Jose Mourinho has publicly expressed his interest in signing the English defender, and the Blues have already had a £20m bid rejected by the Toffees, the Mirror reports, but are yet to return with an improved offer.

"We made a bid, the bid is there and Everton have the power to accept it or refuse it," Mourinho told Sky Sports.

"This is between John Stones and Everton and I don't speak about him because he is an Everton player."

"If we made a bid it is because we like the player, we don't make bids for players we don't like, but we respect Everton and respect every club that has a player and it is up to them - everything is in their hands."

Everton manager Roberto Martinez is adamant that the defender will not be sold, and has criticised the Portuguese manager for his public pursuit of the Everton defender.

Stones joined Everton from Barnsley in 2013 and has gone on to establish himself as the first-choice centre-back under the Spanish manager. His performances have seen him being called up to the senior England squad and Mourinho has identified the 21-year-old defender as the perfect long-term replacement for John Terry, who turns 35 this year.

Manchester United are also said to be interested in signing the defender, according to the Mirror, and will make a move if they fail in their pursuit of Real Madrid's Sergio Ramos.

However, another ESPN report claims that, Chelsea are said to be readying a second bid in the region of £26m to sign the young defender, and are reportedly confident that they can persuade the Merseyside club to sell, as they believe that Stones is keen on a move to Stamford Bridge.